UC Irvine

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential ( n / n ~ e / kT e ~ 0. 5) are observed at the plasma edge, accompanied by a large density gradient (L n = ∇ ln n - 1 ~ 2 cm) and shearing rate ( ~ 300 kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V bias) on the obstacle and the axial magnetic field (B z) strength. In cases with low V bias and large B z, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B z, large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m = 1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge. © 2012 American Institute of Physics.